Three-dimensional structures can be fabricated by a variety of techniques, including machining, stereo-lithography and multi-photon absorption polymerization (MAP). Such three-dimensional structures are often referred to as a “masters” when they are used in a replication process. Replicating masters can be achieved by using transfer molding, or micro-transfer molding (μ-TM) when features to be replicated are small, e.g., less than 500 μm. Micro-transfer molding has been reviewed by Whitesides in Accounts of Chemical Research, 35 (7), 491-499 (2002).
Referring to FIGS. 1A, 1B, 1C and 1D, a mold 30 can be made from a master 10, by pouring a first molding material, e.g., a silicone molding material, e.g., poly(dimethylsiloxane) (PDMS), about master 10, and then allowing the molding material to set, e.g., vulcanize, producing a separable master-mold complex 20. Separation of complex 20 frees master 10 and mold 30. Replica 50 can be prepared from mold 30 by pouring a second molding material, e.g., a polyurethane or an acrylic molding material, into mold 30, and then allowing the second molding material to set, producing a separable replica-mold complex (not shown). Separation of the replica-mold complex frees mold 30 and replica 50. Master 10 can be used a number of times to produce a number of molds, and the resulting molds can be used a number of times to produce a number of replicas.